Link two entities based on unique value not ID

Question

I have the following database tables. Primary keys are ID and AnimalType.Type is a unique string.

Animal
- ID
- Name
- TypeID

AnimalType
- ID 
- Type [Herbivore, Carnivore]

My classes are as follows.

public class Animal
{
    public int ID { get; private set; }

    public string Name { get; set; }

    public AnimalType Type { get; set; }
}

public class AnimalType
{
    private int ID { get; set; }

    public string Type { get; set; }
}

How would I get the following code to work in NHibernate so that it references the same AnimalType of Herbivore?

var horse = new Animal() { Name = "Horse", Type = new AnimalType() { "Herbivore" }};

repository.SaveOrUpdate(horse);

var rabbit = new Animal() { Name = "Rabbit", Type = new AnimalType() { "Herbivore" } };

repository.SaveOrUpdate(rabbit);

UPDATE

Be nice if I could get NHibernate to perform this logic: http://andreas.scherbaum.la/blog/archives/11-Avoid-Unique-Key-violation.html

Answer 1

I'd investigate a few options.

1) If the data doesn't change frequently, can you make AnimalType an Enum instead of an Entity Object?

2) Instantiate an object of the Herbivore AnimalType using animalTypeRepository.FindByType("Herbivore") and pass that object into your new Animal.

3) Move the above logic into the animalRepository.SaveOrUpdate(animal) method so that you'd have...

public class AnimalRepository
{
  public void SaveOrUpdate(Animal animal)
  {
    var animalType = animal.Type;
    if (animalType.ID == 0)
    {
      animal.Type = animalTypeRepository.Find(animalType.Type);
    }

    // save or update animal...
  }
}